Signalling systems for the control of street traffic



Aug. 17, 1965 A. 1.. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Filed May 31, 1960 7 Sheets-Sheet l 4 4 IMRA l AHJ. -e5v MR5 Y' I SADMC L IA WL '2 SADM' N1 I T 2 12 T R14 VTA PBA Nv'QQSJ1 i2 03 110 112 L4 l IG RAO 0A2l AMB GLI -ERA P1 P2 P3 P4 /PAZ I PBZi PCZI PD2 INVENTOR ALA/V 1551 /E RANGE ATTORNEY 17, 1965 A. L. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Filed May 31, 1960 7 Sheets-Sheet 2 5H1 -(B5V 1 ssomc I l TB Essa SBDM N2 Y .3 5& T 12 IBB AM,-oQ5ll l2 l3 LO I12 130 I6 RAO F AMB 6L,

# RA, A, JPJ. P2 P3 P4- BSA ass Faa INVENTOR ALAN LESL E RANGE 7, 1965 A. L. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Filed May 51. 1960 7 Sheets-Sheet s 4 3 evfi R16 VOA asv OFFSET A 3 vos- INVENTOR AMI/v LESLIE RANGE ATTORNEY 7, 1965 A. L. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Filed May 31. 1960 '7 Sheets-Sheet 4 Q2 5% Al N3 1 3 3:45v

INVENTOR ALA/V LESLIE K/I VGE ATTORNEY Aug. 17, 1965 A. L. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Filed May 51, 1960 '7 Sheets-Sheet INVENTOR ALAN LESL/E RANGE BY -91 MM ATTORNEY Aug. 17, 1965 A. L. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Filed May 31. 1960 KEP 7 Sheets-Sheet 6 RAM KLP

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KFA-ON KFA-OFF ALA/V LESZ E RANGE JQW ATTORNEY Aug. 17, 1965 A. L. RANGE 3,201,749

SIGNALLING SYSTEMS FOR THE CONTROL OF STREET TRAFFIC Flled May 51, 1960 7 Sheets-Sheet 7 INVENTOR AMA/v 1552/5 RANGE ATTORNEY United States Patent 3,201,749 SIGNALLING SYSTEMS FOR THE CONTROL 6F STREET TRAFFIC Alan Leslie Range, Liverpool, England, assiguor to Automatic Telephone & Electric Company Limited, Liverpool, England, a British company 7 Filed May 31, 1960, Ser. No. 32,804- (Ilaims priority, application Great Britain, June 26, 1959, 21,932/ 59 10 Claims. (Cl. 340-41) The present invention relates to signalling systems for the controlof street traiiic such as are now widely employed to relieve congestion and promote safety, particularly at busy intersections. The invention moreover is concerned with systems of the type likely to be useful in large cities for the progressive control of a number of intersections which may be spaced along a main trafiic artery or may otherwise be included in a unified control district.

Systems have already been proposed in which vehicle detectors are located in the approaches to the different intersections and exercise some control over the timing of the signals so that automatic adjustment may be made to meet the conditions prevailing at any particular time.

Though this is of advantage in situations where the trailic is often intermittent in that it avoids unnecessary waiting, it may not produce satisfactory results in situations where the traffic is so'heavy as to be substantially continuous but changes'its nature at different periods of the day.

Inthese circumstances the requirements can often be met more satisfactorily by the provision of a so-called fixed time system, that is to say one in which the operation of the signals is not directly controlled by. the vehicles themselves but takes place in accordance with'a predetermined plan. It is by no means essential however that the same plan" should operate throughout the 24 hours and in the circumstances considered,-the best results can probably be obtained by the use ofthree or four plans which are changed as circumstances dictate preferably from a central point inwhich may involve the send ing of signals by radio or over linking cables; plan changing being effected manually. or in some cases by time switch control or in other cases under the control of a computer responsive to representative samples of trailic.

The present invention is concerned with a system of this type inwhich the timing at a plurality of sets of signals is determined by pulses sent from' a master con troller to the controllers at the individual intersections, arrangements being provided whereby it the supply of control pulses should fail for any reason the individual controllers will continue to function with'a slightly longer timing which however is a reasonable approximation to the optimum figure. The chief object of the invention is to provide a simple and inexpensive'system giving. ac curate and flexible timing and permitting the ready introduction of additional facilities-to meet special require-' ments.

According to one feature of the invention in a traffic signalling system for the control of a plurality of intersections in aunified-control district andhaving separate control units provided at each intersection and linked working throughout the district secured by the transmission of control impulses from a master controller to all the local control units simultaneously, a plurality of timing.

3,201,749 Patented Aug. 17, 1965 "ice 2. plans are provided for and the plan to be adopted is determined by a characteristic signal transmitted repeatedly from the master controller to the local control units.

According to another feature of the invention in a trafiic signalling system for the control of a plurality of intersections in a unified control district and having separate control units provided at each intersection and linked working throughout the district secured by the transmission of control impulses from a master controller mall the local control units simultaneously, a plurality of timing plans are provided for and the plan to be adopted is determined by a characteristic signal transmitted from the master controller to the local control units at a point of time which fixes the commencement of one main phase of the cycle.

In a desirable embodiment of the invention the master controller is arranged to send out two pulses per cycle, one at the beginning and another about half-way through, and these serve to determine the end of the two main phases and subsidiary phases may then be introduced it necessary by the individual controllers. Since the signal change will obviously not be required to take place-at each intersection immediately on receipt of the control pulse, each individual controller includes a so-called offset timer for each main phase which determines how soon after the receipt of the pulse from the master controller the appropriate action shall take place. The two offset timers in any one individual controller will be set to the same value and in suitable circumstances their function might be performed by a single timer.

The system also provides for a number of different plans any one of which can be brought into action by suitable operation of the master controller and this is effected by arranging that the first switching pulse from the master controller is in fact in the form of a train of pulses the number of which determines the plan to be followed. This train of pulses is sent each cycle and thus serves to check that the appropriate plan is in fact in action and also serves to change it when any change is required.

Conveniently, use is made in each individual controlled of three electro-magnetically-operated step-by-step switches of the type commonly employed in automatic telephone systems. One of these switches is advanced at appropriate instants under the control of local timing equipment and serves to control the signals for one main phase and any subsidiary phases associated therewith. The second switch similarly controls the operation of the signals during the other main phase and any associated subsidiary phases. The third switch responds to the train of impulses from the master controller for checking or determining the plan and over the wipers of this switch suitable relays are operated which then adjust the various timings as necessary These relays are provided with electrical interlock circuits so that only one relaycan be energised at a time and the operation of a further relay to bring a new plan into action releases the relay previously operated corresponding to the existing plan. Further interlocks are provided in connection with the circuits for the actual signal lamps to ensure that in no case can the green signal be given to two conflicting phases at the same time.

Plan changing is effected as pointed out above at the beginning of the master controller cycle and since the states of the signals are different at the various intersections, it is necessary to ensure that a minimum green period is always given to the phase then possessing right of way in order to give adequate clearance for a vehicle already in the intersection and this is provided for in the local circuits. If the change of plan would involve an unduly long green period at any intersection during the changeover, this can be arranged to be terminated earlier by the local timing in the individual controller on this occasion and thereafter the new plan becomes operative.

In order to give greater reliability in the signalling operation, the first impulse or train of impulses in the cycle is preferably of one polarity and the impulse which occurs at about the middle is of opposite polarity. It will be appreciated that by suitable adjustment of the second impulse within the cycle the ratio of the two main green periods, which is commonly known as the phase split, may be suitably varied. Moreover if the timing periods for the two impulses are both varied in the same direction the cycle time may be changed and this has the advantage that no change is made in the auxiliary periods such as amber timing but only in the right of way periods. This might not be the case if the timing operation were controlled by a motor-operated device with a variable speed. Conveniently manual plan selection at the master station is elfected by operation of the appropriate one of a plurality of locking push buttons which co-operates with a stepping switch which controls the sending of impulses until the position is reached to which the button is connected. Thereupon the transmission of impulses is stopped and the plan control relay in that position remains energised. These plan control relays also are electrically interlocked to prevent the operation of more than one at a time. It is desirable that the push buttons should also be 1interlocked and this is conveniently done mechanical y.

The timings between the different phases and signal changes are effected without undesired variations by the use of an improved electronic timer conveniently employing a thermionic valve which is controlled by the charging and discharging of a capacitor.

Details of one manner in which these arrangements may be carried out are shown in the accompanying drawings comprising FIGS, 1-9. Thus FIGS. 1-4 represent a circuit diagram of an individual controller, FIG. 5 indicating how these figures should be fitted together, \while FIGS. 6-8 represent a similar circuit diagram of a simplified form of master controller and FIG. 9 indicates how they should be fitted together.

It will be convenient to consider first how the controller of FIGS. l4 operates independently, that is to say in the absence of any pulses from the master controller over the linking lines. The operation is controlled by the special electronic timing circuit just referred to and it will be seen that the two main phases are controlled respectively by two electromagnetically-operated stepping switches SA and SB. It will be assumed that when power is first switched on, both of these switches are in the normal position as a result of which relay N is operated. Moreover since the capacitor 01in the A phase timing circuit, FIG. 1, is discharged, the grid of the valve VTA is positive with respect to the cathode and the valve is conducting. Consequently relay TA operates from positive potential (earth) supplied over wiper SB2 in normal position and rectifier MRC. Contacts TAZ are then closed to cause capacitor 01 to be charged by the flow of grid current through the valve and contacts TA l energise the magnet SADM of the switch SA. The DC. supply is obtained from a full-wave rectifier and is unsmoothed so that it constitutes half-wave pulses with the voltage falling to substantially zero between them. The charging of capacitor C1 proceeds during the peaks but between them the existing potential of the capacitor is impressed between grid and cathode, the grid being negative with respect to the cathode. As the potential across C1 increases, a point is reached after six or seven pulses representing only a small fraction of a second when the negative potential is sufiicient to bring about the release of relay TA. The capacitor C7 which is of very small value compared with G1 has a smoothing effect on the gridpulse waveform and helps to stabilise the duration of the output pulse from relay TA. This arrangement whereby the relay is only operated momentarily for a closely controlled period, is found to be more reliable in operation and immune to switching surges than the alternative in which the relay is only released momentarily. The release of relay TA causes the switch SA to advance one step and also owing to the opening of contacts TA2, the charge on the capacitor C1 is now enabled to leak away through the appropriate resistance. The arrows P1, P2, P3 and P4 bracketed as RAO represent strapping connections for the four plans extending to the appropriate terminals of the group .1-30 whereby a suitable amount of resistance is included in the discharge circuit to give the desired timing. Timing at this stage is accordingly through the appropriate red-amber off-set connection and determines the amount of amber stagger to be allowed. At the end of this interval, relay TA again operates and shortly afterwards releases so that the switch SA is advanced to position 3. In this position relay ASA is operated and at contacts ASA2, FIG. 4 lights the amber signal AA to the A phase in addition to the red signal R-A which was lighted together with the phase B red signal R-B when the power was switched on. Timing takes place as before but now over the red-amber connection RA and the switch SA is advanced to position 4 at the end of the period. Thereupon relay ASA releases and ASB operates whereupon the A phase green signal GA is lighted over contacts ASAl and ASBZ to give green to phase A while red is still shown to phase B. The timing is now through the appropriate initial green connection shown bracketed at IG for the different plans and the switch SA then steps to position 5. This movement produces no signal change but starts the timing of the green limit over GL and also wiper SA2 now provides a circuit to enable the off-set A timer to operate as will be more fully described subsequently. At the end of the green limit period, or earlier if the master controller is operating, the switch SA steps to position 6 and wiper SAZ now provides a circuit including rectifier MRE for relay 'IB corresponding to the B phase which is connected in the anode circuit of valve VTB in the same circuit arrangements as relay TA. Switch SB is accordingly stepped to position 2 to time the red-amber olf-set period and thereafter it operates to time the B phase red-amber and green periods in the same manner as just described for switch SA. Switch SA in position 6 times amber to phase A due to the strapping represented by AMB and when this is completed, the switch steps to position 7 in which a circuit is completed for relay AH over its upper winding. Since relay N is now released because both switches are offnormal, a homing circuit is now completed for switch SA and this circuit is opened at contacts AHl when the home position is reached. During this operation contacts AH2 disconnect negative from relays ASA and ASB. It will be noted that a circuit for the lower winding of relay AH is provided over contacts 4 and 5 of wiper SB3 i.e. when green is being shown to the B phase and a similar interlock is provided involving relay BH. These interlocks are desirable to ensure proper operation and prevent the giving of false signals in case either switch should be moved manually, for instance during maintenance operatrons, to a position which would otherwise produce faulty working. Thus for instance if switch SA was in position 4 and switch SB in position 6 when power was switched on, relay BH would be operated to drive switch SB home and Aphase green signals would be given initially.

It Wlll be appreciated that the use of the independently driven switches SA and SB enables additional phases to be readily incorporated between the main phases if this should prove desirable. Such phases might for instance be employed to enable pedestrians to cross or to give an overlap in cases where there was an appreciable amount of turning trafiic. They may readily be incorporated by modifying the wiring of the switch banks and adding further signal relays as necessary. Generally speaking only one switch is in action at a time but there is some overlap to provide the staggered amber facility.

Consideration will now be given. to the arrangements responsive to the linking pulses. As already explained, a series of pulses, the number of which indicates the particular plan in operation, is transmitted at the beginning of each master controller cycle and this eifects the setting of switch SC, FIG. 4. The pulses concerned are in a direction to operate relay A while the single pulse sent about the middle of the cycle serves to operate relay B. These relays are polarised in opposite directions by rectifiers MRI-1 and MRG respectively connected in series therewith across the linking lines L1 and L2. The operation of relay A at contacts A1 energises relay CD which is slow to release and therefore remains operated throughout the train of impulses. Contacts A2 also follow the impulses and thus efiect setting of the switch SC by means of magnet SCDM in a circuit including operated contacts CDl. Contacts CD1 also operate relay AX over its upper winding and this at contacts AXl locks up by way of its lower winding in series with resistor R12 and at contacts AXZ and AX3 prepares for the operation of the off-set A timer which is similar to the timing circuit already described and involves value VOA having relay A in its anode circuit. In this case the normally closed condition of contacts AXZ ensures that capacitor C5 is charged and when these contacts open, it discharges by way of the resistors connected up by the strappings indicated over the contacts of the operative plan relay. The operation of relay 0A is dependent upon wiper SAZ being in position 5 as already described and if this is the case, relay OA operates at the end of the timed period and at contacts 0A1 completes a locking circuit for itself and provides earth if necessary for the operation of relay TA. Contacts 0A2, FIG. 1, provide a quick-step circuit for advancing the switch SA to position 6, thereby terminating the green limit period and initiating the showing of an amber signal. At the same time switch SA completes a circuit for relay TB to permit switch SB to move to position 2 and start the timing of the red-amber off-set period.

On the release of relay CD at the end. of the train of impulses, a circuit is completed over contacts LH3 and wiper SC]. for the appropriate plan relay PA, PB, PC or PD which then completes a locking circuit over its other winding. This is not strictly true of relay PA since its locking circuit extends over normal contacts PB7, PC7 and P337 and thus it is operated as soon as power is switched on. It will be noted that the circuits are such that only one relay can remain operated and consequently the plan is checked each cycle and changed when necessary. The plan relays then connect up the necessary controls for determining the initial green period, the redamber off-set, the off-set A and off-set B period, the contacts concerned for plan A being PA1 and PA3, PA2 and PA E, PAS and PAo respectively. It will be appreciated that plan A will come into operation if, owing to some fault, pulses are not received from the master controller.

When the B pulse is received about half way through the cycle, relay B is operated and at contacts B2 energises relay BX which performs similar functions to relay AX as regards the off-set B timer. This involves valve VOB with relay OB in its anode circuit and the main and auxiliary capacitors concerned are C6 and C11. By the operation of this timer relay OB is operated in due course and by completing a quick step circuit for switch SB at contacts 0132, FIG. 2 terminates the green limit period for the B phase. Relay B also operates relay LH over its lower winding and this relay then locks up over its upper winding and at contacts LHZ completes a homing circuit for the switch SC by way of wiper 8C3, at the same time at contacts LH3 removing earth from wiper SCI to prevent and disturbances of the plan relays. Relays OA and OB also at contacts 0A3 and 0133 provide circuits for short-circuiting and releasing the associated relays AX and BX respectively when both the switches SA and SB are off normal and hence relay N is released.

The circuit arrangement of FIGS. 1-4 also includes a flashing. amber arrangement involving relay F in association with the double triode valve VP. If this facility is to be brought into operation, a train of A impulses is trans mitted which has the effect of operating switch SC to its seventh position, whereupon relay PA is operated over wiper SCI and at contacts FA1 locks up over its left-hand winding and at contacts FAZ operates relay FB. Relay FB then at contacts FBI initiates the operation of the flasher and at contacts FBZ and FB3 energises relays ASA, ASB, BSA and BSB so as to light only the amber lamps. On the operation of contacts FBI, capacitor C3 is charged and since capacitor C4 is discharged, the righthand triode conducts and relay F is operated over its righthand winding. Thereupon at contacts F1 it interrupts the charging circuit for capacitor C3 and completes a charging circuit for capacitor C4. Capacitor C3 discharges through resistor R7 until a grid potential is reached at which the left-hand triode conducts so that current flows through the left-hand winding of relay F. As the two windings are in opposition, the relay now releases, whereupon contacts Fl allow capacitor C3 to start recharging, and capacitor C4, which was charged over these contacts when they were operated, now discharges through resistor R8. In due course therefore the initial conditions are restored and current again flows through the right-hand winding of relay F and the" relay again operates. This cycle repeats as long as relay FB remains operated. Relay-FL is operated on the operation of relay F and at contacts FLl, FIG. 4 interrupts the supply to the amber lamps and thus gives the desired flashing effect. The adjustable trimmer resistors TFP and TFM permit adjustment of. the flashing period and also some control over the make-break ratio. Capacitor C9 across the righthand winding of relay F tends to nullify the effect of the ripple on the supply. Resistor R6 provides a small initial current through the right-hand winding of relay F and thus facilitates the operation of the relay.

It will be seen that if the switch SC is setto theeighth position by a suitable train of A impulses, relay FA will be short-circuited and released so that the flashing amber condition will be terminated and the previously operated plan relay will resume control.

It is assumed that each individual controller will be provided with a facility switch which is preferably mounted on the control pillar and operable by a key. This is shown as having four positions and is represented by the arcs PSI-4. Position 1 is the off position in which operation of the signals will not take place, position 2 corresponds to normal automatic operation, position 3 enables operation to take place under the control of the manual push buttons PBA and PBB, while position 4 causes the operation of relay FB over are PS3 and thus introduces flashing amber in place of the normal red and green signals.

It may be mentioned that the trimmer resistors TTA, TTB, TOA, TOB associated respectively with the various timing circuits serve to permit some measure of adjustment to secure the best operating conditions.

Considering now the master controller illustrated in FIGS. 6-8, this also includes a stepping switch M which is shown as of the 25-point type as opposed to the 12- pointv type used in the circuits of FIGS. 1-4. This controller also includes an electronic timer of the same type as employed in the individual controllers, this comprising a double triode VIT having its two halves connected in parallel and employing main and auxiliary capacitors 1C1 and 1C2 in the grid circuit. The circuits-are arranged so that relay lT connected in the anode circuit enemas of the valve is momentarily operated twice per cycle at intervals which can be adjusted by the manually operated switches shown. It is assumed that four plans are provided which cater for light, medium and heavy trafiic and for emergency operation and have associated plan relays IPA-119D respectively. The manually perable switches LA, MA, HA and EA for the various plans give coarse adjustment of the timing in that they alter the discharging resistors so as to produce variation in ten-second steps. The switches LB, MB, HB and EB similarly give fine adjustment by altering the resistors in steps corresponding to two-second intervals. In addition the phase split is determined for the two mam phases by the manually operable switch having the two wipers P881 and P852 which adjusts the relative lengths of the A and B phases without altering the cycle time. Alternatively these adjustments may also be made automatically by electrically-operated devices such as stepping switches which are controlled from a vehicle density computer to which information is transmitted from strategic points.

Pulses from relay 1T cause relays 1A and IE to be operated in turn. Thus when contacts 1T2. first close, relay 1A is operated over its lower winding and at contacts 1A2 prepares a circuit for the lower winding of relay 1B. When contacts 1T2 open, relays 1A and 1B are held in series by way of their lower windings. When contacts 1T2 next close, the upper windings of relays 1A and 1B are energised in series and relay 1A is then released since its windings are connected in opposition. Relay 1B is maintained until the end of the pulse however over contacts 1B2, 181 and 1A1 and releases when the pulse ceases, thus restoring the original conditions.

With relay 1B unoperated, contacts 1T3 complete a circuit for the upper winding of relay 1ST which is arranged to be slow to release and this then at contacts 1ST2 completes a circuit for the magnet MDM of the switch M in series with the magnet interrupter springs MDMC. On the operation of these springs, the shortcircuit is removed from the lower winding of relay IP and it operates in series with the magnet. Thereupon at contacts 1P1 it transmits a pulse over the linking lines L1 and L2 by way of operated contacts 1ST3 and 1ST4 and at contacts 1P2 operates relay 1CD and provides a holding circuit for relay 1ST over contacts 1ST1. Relay 1CD thereupon at contacts 1CD1 opens the magnet circuit so that the switch steps to the next position and relay 11 is released. Since there is no marking picked up by wiper M2 in this position, relay 1CD releases and again completes the magnet circuit so that relay IP is again energised and re-operates relay 1CD and sends a further pulse over the linking lines. This operation continues until wiper M2 encounters earth due to the operation of one of the plan switches. When this occurs, relay 1CD is maintained over its lower winding and relay 1ST releases, thereupon energising relay lMH over wiper M1. This by closing contacts IMHZ drives the switch M to its home position and at contacts lMHl removes earth from wiper M3 to ensure that there shall be no further operation of the plan relays IPA-IPD which with the circuits shown will have been operated in turn as the switch stepped.

When relay 1T next operates, relay IE will be operated and at contacts 133, FIG. 6, changes over the timing connections so as to correspond to the B phase and at contacts 1B4 causes the operation of relay 1P to transmit a further pulse over the linking lines L1 and L2. Since relay ST is not operated on this occasion however, the pulse is in the reverse direction to those previously sent and also there is no circuit provided for stepping the switch M. Accordingly only a single pulse is sent and relays 1A and 1B are then both released.

It will be noted that keys or push buttons KLP, KMP and KHP when operated effect suitable markings in the bank of wiper M2 so as to bring the switch to rest in the appropriate position as just described and thus energise the corresponding plan relay. These relays are connected in the same manner as the corresponding relays shown in FIG. 4 in an individual controller so that only one can be operated at a time and relay IPA is operated when power is first switched on. The three keys are preferably mechanically interlocked so that the operation of any one releases the others. Key KEP for the emergency plan may conveniently not be interlocked so that when it is operated, though it removes the operating earth from the other keys, it does not release them. Hence when the key KEP is restored, the plan previously in operation is again effective. It is assumed that the emergency plan would be required for only a short period in special circumstances and as illustrated, the emergency plan relay PD, FIG. 4, at contacts PDS, FIG. 1, prevents the termination of the A phase, and at contacts PD9, FIG. 2, at once terminates the B phase after the initial green interval has expired. This means that the A phase, assumed to be the main road, retains right of way and no traflic can emerge from the side streets. Such a method of working might be required on special occasions such as a procession or to permit the safe uninterrupted passage of fire engines or other priority traflic.

The auto/manual key KAM permits changeover from manual operation as controlled by the keys to automatic operation under the control of the automatic timing equipment ATE which is assumed to connect up the ditferent plans on a predetermined time schedule. Keys KFA-ON and KFAOFF control respectively the commencement and termination of flashing amber workmg.

Lamps are preferably provided as shown to indicate which plan is in action. Thus lamp LLS corresponding to the light traffic plan is connected up by the corresponding plan relay IPA at contacts IPAZ and similarly for the lamps LMS, LHS and LES. Lamp LPS serves as a pilot lamp to indicate that the equipment is in operation.

It will be appreciated that the arrangements associated with the master controller may be suitably varied to meet different requirements. For instance the number of plans may be increased if necessary and provision need not be made for the emergency plan as described, particularly if the unified control system covers an area rather than a single main road moreover as previously suggested the control equipment represented by ATE in FIG. 7 need not be merely time-controlled but may comprise or include some form of computing equipment directly responsive to the density of traflic at suitable sampling points.

I claim:

1. In a street trafiic signalling system, a master controller, a plurality of local controllers respectively associated with intersections on a main highway, a signaling line extending from said master controller to each of said local controllers, a plurality of sets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for transmitting simultaneously from said master controller to said local controllers a discrete signal of one type for initiating the termination of the right-of-way period accorded by said visual signals to traflic on said main highway, means for transmitting simultaneously from said master controller to said local controllers a discrete signal of a different type for initiating the termination of the right-of-way period accorded by said visual signals to traffic on streets crossing said main highway, and timing devices in said local controllers which are set in operation in response to said signals and serve to control said visual signals to terminate said right-of-way periods respectively on completing their operation.

2. In a street tratfic signalling system, a master controller, a plurality of local controllers respectively associated with intersecting trafiic lanes in a unified control district, a signalling line extending from said master controller to each of said local controllers, a plurality of ets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for transmitting simultaneously from said master controller to said local controllers a signal for initiating the termination of the right-of-way period accorded by said visual signals, a timing device in each of said local controllers arranged to control said visual signals to terminate a right-of-way period on completing its operation, first control means for said timing device effective in response to said signal to cause said timing means to complete its operation after a first predetermined period, and second control means for said timing device effectively independently of said signal to cause said timing device to complete its operation after a second predetermined period which is longer than said first predetermined period so as to terminate said rightof-way period if said signal is not received.

3. In a street traffic signalling system, a master controller, a plurality of local controllers respectively associated with intersecting trafiic lanes in a unified control district, a signalling line extending from said master controller to each of said local controllers, a plurality of sets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for transmitting simultaneously from said master controller to said local controllers a discrete signal of variable characteristics for initiating the termination of the right-of-way period accorded by said visual signals, timing devices in said local controllers which are set in operation in response to said signal and serve to control said visual signals to terminate a n'ght-of-way period on completing their operation, discriminating means in said local controllers selectively responsive to the different characteristics of said signal, and means controlled by said discriminating means for altering the eriod of operation of said timing devices to produce signal changes in accordance with any one of a plurality of different plans.

4. In a street trafiic signalling systems as claimed in claim 3, means controlled by said discriminating means for nullifying the operation of said timing devices whereby right-of-way is given indefinitely.

5. In a street trafl rc signalling system as claimed in claim 3, means controlled by said discriminating means for modifying the operation of said visual signals so as to give a continuous flashing Warning signal.

6. In a street traflic signalling system, a master controller, a plurality of local controllers respectively associated with intersecting traffic lanes in a unified control district, a signalling line extending from said master controller to each of said local controllers, a plurality of sets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for repeatedly transmitting simultaneously from said master controller to said local controllers a discrete signal of variable characteristics for initiating the termination of the right-of-way period accorded by said visual signals, timing devices in said local controllers which are set in operation in response to said signal and serve to control said visual signals to terminate a right-of-way period on completing their operation, discriminating means in said local controllers seiectiveiy responsive to the different characteristics of said signal, and means controlled by said discriminating means for altering the period of operation of said timing devices to produce signal changes in accordance with any one of a plurality of different plans.

7. In a street trafiic signalling system, a master controller, a plurality of local controllers respectively associated with intersecting traffic lanes in a unified control district, a signalling line extending from said master controller to each of said local controllers, a plurality of sets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for transmitting simultaneously from said master controller to said local controllers on each signalling cycle a discrete signal of variable characteristics for initiating the termination of the right-of-way period accorded by said visual signals, timing devices in said local controllers which are set in operation in response to said signal and serve to control said visual signals to terminate a right-of-way period on completing their operation, discriminating means in said local controllers selectively responsive to the different characteristics of said signal, and means controlled by said discriminating means for altering the period of operation of said timing devices to produce signal changes in accordance with any one of a plurality of different plans.

3. In a street trafiic signalling system, a master controller, a plurality of local controllers respectively associated with intersecting traific lanes in a unified control district, a signalling line extending from said master controller to each of said local controllers, a plurality of sets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for transmitting simultaneously from said master controller to said local controllers a signal comprising a variable number of impulses which signal serves to initiate the termination of the right-of-way period accorded by said visual signals, timing devices in said local controllers which are set in operation in response to said signal and serve to control said visual signals to terminate a right-of-way period on completing their operation, discriminating means in said local controllers selectively responsive to the number of impulses comprising said signal, and means controlled by said discriminating means for altering the period of operation of said timing devices to produce signal changes in accordance with any one of a plurality of different plans.

9. In a street traffic signalling system, a master controller, a plurality of local controllers respectively associated with intersecting trafiic lanes in a unified control district, a signalling line extending from said master controller to each of said local controllers, a plurality of sets of visual signals respectively controlled by said local controllers and arranged to selectively accord and deny right of way, means for transmitting simultaneouly from said master controller to said local controllers a signal comprising a variable number of impulses which signal serves to initiate the termination of the right-of-way period accorded by said signals, timing devices in said local controllers which are set in operation in response to said signal and serve to control said visual signal to terminate a right-ofiway period on completing their operation, a multi-contact step-by-step switch in each of said local controllers selectively responsive to the number of impulses comprising said signal, and means controlled over the contacts of said step-by-step switch for altering the period of operation of said timing devices to produce signal changes in accordance with any one of a plurality of different plans.

10. In a street traffic signalling system, a timing device for determining the duration of the different signalling periods, comprising a thermionic valve having cathode, anode and grid electrodes, a relay connected in the anode circuit of said valve, a source supplying unsmoothed rectified alternating current, a capacitor conected to the grid of said valve, a variable resistor, circuit connections for causing said capacitor to be discharged through said resistor and said relay to be operated when said discharging operation has taken place to a predetermined extent, contacts closed due to the operation of said relay for causing said capacitor to be charged by the flow of grid current during the peaks of said supply current until said valve is again cut oil and said relay releases whereby said relay is operated for a predetermined period and the time required for the re-operation of said relay is dependent upon the value of said resistor.

References (Iited by the Examiner UNITED STATES PATENTS Barker 340-40 Schulenburg 340-40 Hendricks 340-40 Wilcox 34040 2/60 Iefiers 340-40 2/60 Masten 34040 OTHER REFERENCES NEIL C. READ, Primary Examiner. BENNETT G. MILLER, Examiner, 

1. IN A STREET TRAFFIC SIGNALLING SYSTEM, A MASTER CONTROLLER, A PLURALITY OF LOCAL CONTROLLERS RESPECTIVELY ASSOCIATED WITH INTERSECTIONS ON A MAIN HIGHWAY, A SIGNALING LINE EXTENDING FROM SAID MASTER CONTROLLER TO EACH OF SAID LOCAL CONTROLLERS, A PLURALITY OF SETS OF VISUAL SIGNALS RESPECTIVELY CONTROLLED BY SAID LOCAL CONTROLLERS AND ARRANGED TO SELECTIVELY ACCORD AND DENY RIGHT OF WAY, MEANS FOR TRANSMITTING SIMULTANEOUSLY FROM SAID MASTER CONTROLLER TO SAID LOCAL CONTROLLER A DISCRETE SIGNAL OF ONE TYPE FOR INITIATING THE TERMINATION OF THE RIGHT-OF-WAY PERIOD ACCORDED BY SAID VISUAL SIGNALS TO TRAFFIC ON SAID MAIN HIGHWAY, MEANS FOR TRANSMITTING SIMULTANEOUSLY FROM SAID MASTER CONTROLLER TO SAID LOCAL CONTROLLERS A DISCRETE SIGNAL OF A DIFFERENT TYPE FOR INITIATING THE TERMINATION OF THE RIGHT-OF-WAY PERIOD ACCORDED BY SAID VISUAL SIGNALS TO TRAFFIC ON STREETS CROSSING SAID MAIN HIGHWAY, AND TIMING DEVICES IN SAID LOCAL CONTROLLERS WHICH ARE SET IN OPERATION IN RESPONSE TO SAID SIGNALS AND SERVE TO CONTROL SAID VISUAL SIGNALS TO TERMINATE SAID RIGHT-OF-WAY PERIODS RESPECTIVELY ON COMPLETING THEIR OPERATION. 